Scatter graphics: Premier League, 2020-21
Now that the season is over (barring play-offs which I exclude for consistency), I can create final versions of the scatter graphics. These compare the attacking and defensive performances of every team in a division – each of the four graphics is explained briefly below and at length here.
First of all, here is how the number of shots taken by each club compares with those they face in return. The average number of shots taken per match is on the horizontal and the average number faced is on the vertical, so bottom right (take plenty, allow few in return) is good while top left (take few, allow plenty) is bad. The stripes are like contours: the greener the stripe, the better the performance (and vice versa for red).
The trio of Man City, Liverpool and Chelsea were comfortably the most dominant overall – at least in shot terms. Brighton out-shot their opponents at a similar level to the other two teams in the top five, yet somehow finished 16th, while Fulham were relegated despite creating more chances than they allowed. Leeds and Aston Villa matches were far from dull.
Now let’s look at attacking alone. The horizontal axis stays the same as in the graphic above, but now the vertical shows the average number of shots needed to score each league goal. Therefore bottom right is good (taking lots of shots and needing fewer efforts to convert) and top left is bad:
Fulham‘s relegation despite creating a respectable number of chances can be at least partly explained by their woeful finishing – even worse than that of bottom club Sheffield United. Tottenham – the division’s most clinical finishers – scored more than twice as many goals from an almost identical number of attempts.
Next let’s look at the defensive situation – basically take the above chart and replace the word “taken” for “faced” on both axes. Now top left is good – facing fewer shots and able to soak up more per goal conceded – and bottom right is bad:
Meanwhile, Southampton‘s poor showing this season looks to have had more to do with a leaky defence: they allowed their opponents a fairly average number of shots but almost one in six found their net. By comparison, Aston Villa allowed almost three more attempts at their goal per match but were able to repel them more successfully and conceded 22 fewer goals.
Finally here’s an attempt at correcting the first graphic for the quality of chances created and allowed, using the same “expected goals” values that power my shot timelines (explained here). The reason for doing this is that the results tend to correlate more strongly with performance than when we treat all shots equally:
When we adjust for shot quality, the same three teams lead the way – it looks like Chelsea are equipped to challenge Liverpool and Man City for the title next season. There are reasons for concern at Crystal Palace, who were the worst-performing side to escape relegation, while Brighton should be able to target a much higher league finish.